Help With Annoying Noise Please

[jason_h 0]

hi, ive just started doing mobile discos on my own after a few years with working with someone.

i have just gone and spent lots an lots of pennys and have encounted a big headache.

i will appoligise for the long post but like to explain things in detail

this is what i got on the audio side:

1 kam kap1000 mixer

1 kam khd2000 hard drive player

1 cortex hdc1000 hardrive player

2 warrior l300 active speakers.

6mtr x2 jack cable (mixer to each speaker)

custom flight case

 

the story behind the mixer was i got it 2nd hand because 1 channel was not working. turns out it was just a faulty line/phono switch. all fixed.

 

now all hocked up, when the mixer master is on 3/4 volume and speakers are on 1/2-full i get a low hum and a hi pitched interference sound. this is only when the cortex is on.

the kam player works fine. when i turn on the cortex u hear the hard drive spin up throu the speakers and the a constant variable squeel.

i have tried ferrite coils and ground loop isolaters but to no avail.

also the sound quality from the cortex distorts noticablly more than the kam.

i have also tried differend hard drives and same problem. tried different leads and also plugged in different lines.

also because you can run a cortex without a mixer (you can use the pitch controls as a volume) i hocked it up to the speakers direct. works perfect.

please help as im going insane :wall:

thanks

[Dukesy 0]

Does the Cortex operate from a seperate external power supply / Mains Adaptor or is the power supply built into the actual unit?

 

I would suspect that the Power Supply is either failing or a component like a Capacitor has failed or gone 'dry' and this is introducing mains and operating interference into the sound chain

 

If the Power Supply is external - i.e like on a laptop, then see if you can get / borrow a replacement of the same voltage and rating and try that. If the power supply is internal and built into the unit, then its probably a case of getting it repaired locally.

[jason_h 0]

Does the Cortex operate from a seperate external power supply / Mains Adaptor or is the power supply built into the actual unit?

 

I would suspect that the Power Supply is either failing or a component like a Capacitor has failed or gone 'dry' and this is introducing mains and operating interference into the sound chain

 

If the Power Supply is external - i.e like on a laptop, then see if you can get / borrow a replacement of the same voltage and rating and try that. If the power supply is internal and built into the unit, then its probably a case of getting it repaired locally.

 

thanks for the reply, i had that problem before on audio with a faulty power supply so that was one of my ideas.

but i tried a new power supply and doesnt do any difference.

oh and it is an external 1 (6v 2000mA)

 

[superstardeejay 0]

It sounds like a ground loop. You say youve tried an isolator, where did you put it.

 

[Derek Paul 0]

It sounds like a ground loop. You say youve tried an isolator, where did you put it.

 

 

I agree definitely sounds like a “Ground Loop”. I had the same problem and a pair of Ground Loop Isolators cured it for me. Look at the link below (to Amazon), and remember you will need an Isolator for each input. I use a Denon HC4500 so I have two isolators, one for each channel.

 

http://www.amazon.co.uk/ground-loop-isolat...ator&page=1

[gadget 0]

I agree definitely sounds like a “Ground Loop”. I had the same problem and a pair of Ground Loop Isolators cured it for me. Look at the link below (to Amazon), and remember you will need an Isolator for each input. I use a Denon HC4500 so I have two isolators, one for each channel.

 

http://www.amazon.co.uk/ground-loop-isolat...ator&page=1

 

 

I'm surprised the HC4500 needs an isolator as it's not got an earth, but I guess your laptop has, so the ground loop will go through the USB cable to the Denon and then to the line outs from there...

 

My ground loop problem was solved by buying an un-grounded (2-pin input/Class 2) PSU :) another random thing is that my mixer has an earthed IEC lead input, but is actually a Class 2 device (no actual earth used)...

 

Anyway, bnack to your probolem..

 

If you have a "ground lift" switch on your active speakers, try flicking that to "lift" instead of ground and see if that cures anything at all ?

 

 

Cheers,

 

David

 

ps. I was given a pair of ground loop isolators but never needed to use them in anger, yet :)

Edited January 29, 2011 by gadget

[jason_h 0]

hi all, thanks for your replys.

ive tried a ground loop on the cortex outputs an this helped a little with the noise, tried it on the output from mixer to speakers and didnt make a difference.

no lift switch to try

 

also the distortion concerns me only on the cortex.

i got a mates behringer vmx1000 to try tomorrow to with my system at least that way i can rule out the cortex.

out of interest has anyone had a compatability problem with kam mixers?

my mate runs a numark c1 with 2 cortex an not a problem.

 

[superstardeejay 0]

Dont forget that you can create parallel ground loops via the rack mounting holes in the case. If anything shares the same rack as the cortex then even the best loop isolators wont stop it as it will be firmly and effectively grounded by its rack screws!!

You can get isolating mounting kits for these in conjunction with the phono lead isolator.

 

 

 

 

[jason_h 0]

hi, yea i tried taking the cortex out but no difference.

anyway think ive gotton to the problem.

tried the beringer, and sucess!, a little noise but only heard when no music playing and everythings turned right up. to be honest the fans in my scanners make more noise.

tried his cortex 3000 with my kam mixer and noise.

opened up my mixer and i had bridged the switch for line and phone on one channel with solder by mistake when i replaced switch. cleaned it up an again sucess but again just a little noise.

then i thought maybe its the jack leads picking up interference, so i tried xlr to the powered cabs and now all i get is a little hiss which i can deal with.

so didnt need the ground loop isolaters after all

 

thanks everyone for your help :Thumbup:

 

[gadget 0]

Yay! Well done for fixing it.

 

You'll always get some minor background hiss - but you've solved your problem, and spare isolator loops in case you imght need them another day!

 

Cheers,

 

David

[jason_h 0]

yep. would i be right in thinking that active speakers will pick up more noise than passive ones due to the length of line level cable?

also wouldnt xlr cable help because its balanced and better screening?

[superstardeejay 0]

i had bridged the switch for line and phone on one channel with solder by mistake when i replaced switch.

 

You didnt tell us you'd been messing!!

 

:wall:

[jason_h 0]

You didnt tell us you'd been messing!!

 

:wall:

i did say in my first post the mixer was faulty, needed a new switch :yes:

funny how annoying things can be created by ones accident :aa

[gadget 0]

You didnt tell us you'd been messing!!

 

:wall:

 

Like you, I totally didn't read one of the lines properly in the original post! :wall:

 

"the story behind the mixer was i got it 2nd hand because 1 channel was not working. turns out it was just a faulty line/phono switch. all fixed."

 

 

Ahh well... The main thing is it's all working now ;)

Edited February 1, 2011 by gadget

[jason_h 0]

Like you, I totally didn't read one of the lines properly in the original post! :wall:

 

"the story behind the mixer was i got it 2nd hand because 1 channel was not working. turns out it was just a faulty line/phono switch. all fixed."

Ahh well... The main thing is it's all working now ;)

sorry probably my fault for not explaining it very well. :hurt: :sad:

[djmick 0]

I used to use isolaters when i first started using laptops, (acers), but having since bought some new lappys the problem has gone away, must be better quality power supplys i reckon,,

[Megasong 0]

One of the most common problems we come across with noise is caused by the switch mode power supplies so often used with lap tops as well as computers in general and sometimes big time with iPads.

 

Depending on the PC this can be really intrusive. It sounds a bit like a whispering and will often increase when the PC is under load. If you are using a laptop or other battery device and the noise disappears when you unplug the PSU you know what it is.

 

Sometimes you get a 'beat' frequency between two switch mode PSUs supplying different pieces of equipment. This can sometimes appear at a low frequency and be reminiscent to mains hum. It's very easy to go off on a wild goose chase here trying to find a non existent earth loop. You can easily see if this is the case with a scope on the input to your amp (assuming it's not a switch mode PSU in there too, because these can beat with other signals as well - a nightmare to trace and cure without the right equipment).

 

Sometimes the signal will creep in through the mains from a completely non sound related piece of kit. All you can do is plus things in one by one until you get the interference then scope it to see what's going on. Not a job you can do without the right test equipment and knowledge unfortunately.

 

There are ways of getting rid of the noise but often it is drowned out by the music and people are unaware of it so I guess to some it doesn't matter. We always try to get our set-up silent and would recommend it as the right way.

 

It is possible to get well smoothed PSUs for Desktop PCs, they tend to cost about triple the price but are worth it. If you are electronically inclined you can also build your own smoothing circuits, basically a choke and capacitors in each of the DC voltage lines. We have done this for Dell and Acer Laptops as well as iPads which seem to be really bad for interference. It involves chopping the supply line to the PC and introducing the smoothing stuff in a box in the line so will invalidate any PSU warranty but it totally efffective.

 

The point of all this is that it is VITAL to check your proposed purchase with your other equipment BEFORE shelling out your cash, or be prepared to add smoothing afterwards. Get friendly with a local electronics person if you can unless you have your own people available. It's a big subject and fortunately not one everyone comes across as most noise is easily disposed of, but when it does bite you it can be a real problem.